In the company brochure PTT 01 P65/04.99 of Lurgi Zimmer AG it is provided to charge a paste consisting of pure PTA and PDO together with a special catalyst into a first reaction pressure stage for esterification. The vapors formed in the esterification and containing PDO, water, acrolein, allyl alcohol, 1-butanol, lpropanol, hydroxypropanol and acetic acid are rectified, the PDO obtained as bottom product being recirculated to the esterification stage and the lower-boiling components being discharged as top product and condensed. An aliquot of the vapor condensate formed is recirculated to the rectification and only the excess aliquot is discharged and subsequently purified. In a second reaction pressure stage, the polymer esterified for 90 to 95% is converted completely and then charged to a first and subsequently to a second prepolycondensation stage, in which low-molecular PTT is formed and PDO is separated. In the subsequent polycondensation stage, PTT is brought to the desired molecular weight. The lower-boiling components obtained in the two condensation stages, preferably acrolein and allyl alcohol, are rectified together with the vapors from the esterification.
From EP-A-0 812 337 it is known to mix the condensed top-product obtained during the rectification of vapors from the production of PTT along with further acrolein-containing waste-waters with a base in a tank, in order to reduce the content of free toxic acrolein. After this treatment, the liquid can be supplied to an aerobic-biological waste water processing. It is particularly disadvantageous that in this process the amounts of acrolein, allyl alcohol, etc. contained therein are not reduced by the addition of alkaline compounds, so that large amounts of “bound” acrolein, free allyl alcohol, etc. are discharged to the biological waste water purification, which results in the production of corresponding amounts of biological excess sludge. Furthermore, toxic effects of the allyl alcohol on the microorganisms in the waster water purification cannot be excluded. Moreover, the exhaust air streams obtained during the production of PTT according to this process are discharged to the atmosphere unpurified.